It is well documented that flexible polyurethane foam is produced from: a polyol, an isocyanate, water, a catalyst, and a surfactant. Polyol and isocyanate are mixed to form a polyurethane linkage. Water is present as a blowing agent and an aqueous medium. Additives, catalyst and surfactant serve to promote nucleation, stabilization of the foam formation during the development stage, and improve foam properties for commercial application.
Polyurethane properties in flexible foam are influenced by the types of isocyanate and polyols used. The most commonly used isocyanates are aromatic diisocyanate or methylene diphenyl diisocyanate (MDI). Polyols can be polyether polyols or polyester polyols. Polyether polyols are made by the reaction of epoxides with an active hydrogen containing starter compounds. Examples of polyether polyols, among others, are: propylene glycol, 1,3-butanediol, 1,4-butanediol, ethylene glycol, neopentyl glycol, 1,6-hexane diol, diethylene glycol, glycerol, diglycerol, pentaerythritol and trimethylol propane and similar low molecular weight polyols. Polyester polyols are formed by polycondensation of multifunctional carboxylic and hydroxyl compounds. In addition to the polyether and polyester polyols, polymer polyols can be used in flexible polyurethane foam to increase foam resistance to deformation. There are two types of polymer polyols: a graft polyol and a polyurea modified polyol. In addition, some polyols that exist commercially are natural oil polyols. These oleochemical polyols have good hydrophobicity and exhibit excellent hydrolysis resistance, chemical resistance and UV resistance. With the presence of a crosslinker, these natural oil-based polyols (i.e. Sovermol® (BASF)) form a polyurethane by linking with an isocyanate. Natural oil polyols are polyfunctional alcohols based on renewable raw materials like castor oil, soybean oil and palm kernel oil, dipropylene glycol or glycerine which are often added as initiators to produce polyols for more flexible applications. Propylene oxide and/or ethylene oxide are then added to the initiators until a desired molecular weight is achieved. The order and amounts of each oxide affect many polyol properties such as water solubility and reactivity.
In general, polyurethane foam is made using organic polyisocyanates such as phenylene diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, or 4,4-diphenyl-methane diisocyanate (MDI).
Flexible polyurethane foam is a common material used to protect objects from impact forces such as in athletic activities, automotive applications, and boating applications. Such foams are lightweight and contain small pores that allow foam to deform elastically under impact so that energy is absorbed and dissipated as the material is compressed. However, flexible foams can only be customized to respond to a very specific range of impact energies and hence generally cannot perform well across a wide range of impact types. A foam that is too soft for an impact will compress too quickly and transmit excessive force to an impacted body. Localized compression of a flexible foam decreases the area over which force is transmitted and therefore increasing pressure and damage of the impact. A foam that is too hard for a specific type of impact will not compress sufficiently and will decelerate the impacted body too quickly. This results in excessive resistance in the early phase of impact and will not compress enough to prolong distance or time of impact. Therefore, advances in impact foams continue to be sought that exhibit light weight, resilience, and desirable impact response to a variety of impact types.
Silicone resins are common and used in various applications due to their superior properties in heat and chemical resistance, electrical insulation properties, water repellency and safety to humans.